What does the FD column specified in lsof mean?
I am using the following command to get a list of channels:
lsof | grep PIPE
I want to know what the FD column values mean (fifth http://i.imgur.com/KHczptf.png ). I think r
both w
mean to read and write , respectively, but what does the number that follows each of those characters mean?
I know FD stands for File Descriptor, I want to figure out what the values shown in the column mean, such as 3r, 16w, 20r, etc.
source to share
Files are opened not only as streams. Some of them are listed in the manual lsof
:
FD is the File Descriptor number of the file or:
cwd current working directory;
Lnn library references (AIX);
err FD information error (see NAME column);
jld jail directory (FreeBSD);
ltx shared library text (code and data);
Mxx hex memory-mapped type number xx.
m86 DOS Merge mapped file;
mem memory-mapped file;
mmap memory-mapped device;
pd parent directory;
rtd root directory;
tr kernel trace file (OpenBSD);
txt program text (code and data);
v86 VP/ix mapped file;
FD is followed by one of these characters, describing the
mode under which the file is open:
r for read access;
w for write access;
u for read and write access;
space if mode unknown and no lock
character follows;
'-' if mode unknown and lock
character follows.
The mode character is followed by one of these lock charac-
ters, describing the type of lock applied to the file:
N for a Solaris NFS lock of unknown type;
r for read lock on part of the file;
R for a read lock on the entire file;
w for a write lock on part of the file;
W for a write lock on the entire file;
u for a read and write lock of any length;
U for a lock of unknown type;
x for an SCO OpenServer Xenix lock on part of the
file;
X for an SCO OpenServer Xenix lock on the entire
file;
space if there is no lock.
See the LOCKS section for more information on the lock
information character.
The FD column contents constitutes a single field for pars-
ing in post-processing scripts.
source to share
This is a file descriptor.
More about this:
The file descriptor (FD) is an abstract indicator for file access. This term is commonly used in POSIX operating systems.
In POSIX, a file descriptor is an integer, in particular of type C. There are three POSIX standard file descriptors, corresponding to the three standard streams that every process is supposed to have (with the possible exception of the daemon).
source to share